The present invention relates to an arrangement for regulating the flow of a gaseous medium in a conduit in general, and more particularly to an arrangement of this type wherein the amount of the gaseous medium permitted to flow through the conduit is controlled in dependence on the pressure of the gaseous medium.
There are already known several arrangements of the above-mentioned type. In some of these arrangements, a flap valve is mounted in the conduit for pivoting between an open and a closed position, is urged toward its open position by a spring, and is urged towards its closed position by the action of the flowing gaseous medium thereon. So, for instance, it is already known to mount the flap valve on a shaft which is located close to but offset from the axis of the conduit, and to construct the flap valve with two sections which are integral with one another and each of which extends to one side of the shaft, these two sections enclosing an obtuse angle with one another. The gaseous medium will exert a different force on each of these sections, owing to the offsetting of the shaft and the angular configuration of the flap valve. In this manner, the flap valve will gradually approach its closed position as the pressure of the gaseous medium upstream of the flap valve increases.
Experience with conducting systems for gaseous media has shown that such systems are always prone to resonate at certain frequency ranges, for instance, due to excitation of oscillations due to periodic detachment of the flow at certain locations of the conducting system. The excitation and resonance conditions occur, as a rule, in certain pressure and through-put ranges.
The resonance oscillations have the unpleasant consequence that the function of the flow-regulating arrangement is detrimentally influenced. They cause the regulating flap valves, which should automatically adjust themselves to the equilibrium between the spring force acting on the respective flap valve, on the one hand, and the forces which the flowing gaseous medium subjects the flap valve, and which should remain in this adjusted regulating position until any change occurs in the forces to which the flowing gaseous subjects the valve, to flutter or oscillate about this adjusted regulating position.
This undesirable phenomenon is of particular significance in the regulating arrangement according to the U.S. Pat. No. 3,965,928, inasmuch as this regulating arrangement is characterized by an extraordinarily high sensitivity to pressure variations. Therefore, there were already proposed, in the U.S. Pat. Nos. 3,996,961 and 4,124,037, certain measures for avoiding or at least damping the fluttering or oscillating movement. These measures have been proven to be effective under many circumstances. So, for instance, if the conduit diameter is less than 100 mm, these measures are sufficient under most circumstances. However, it has been established that once the conduit dimensions, and hence the dimensions of the flap valve, are greater than that, and especially when the diameter of the conduit is between 140 mm and 160 mm, the flap valve has nevertheless a certain tendency to "float", so that further damping means have to be provided.
There are already known pneumatic damping members which could be utilized for this purpose. These damping members which, for instance, include a pneumatic cylinder which is equipped with a throttled air supply and discharge are, however, expensive and relatively sensitive.